Molecular genetic characteristics of mcr-9-harbouring Salmonella enterica serotype Typhimurium isolated from raw milk

Int J Antimicrob Agents. 2021 May;57(5):106332. doi: 10.1016/j.ijantimicag.2021.106332. Epub 2021 Mar 30.

Abstract

Among the 10 reported mcr genes, mcr-9 was first identified in Salmonella enterica serotype Typhimurium, which is a leading cause of foodborne illness worldwide. However, information about the prevalence and genetic features of mcr-9 is still lacking, especially among food samples. This study reports the presence of mcr-9 in raw milk samples from China; the prevalence rate was low (0.83%, 1/120). mcr-9 was located on a transferable plasmid, and was stable in wild-type S. enterica. However, it had a biological fitness cost when transferred to an Escherichia coli recipient. Whole-genome sequencing revealed that mcr-9 was located on the IncHI2A-type plasmid, and was surrounded by IS903B and IS26 in its flanking regions. The mcr-9-carrying S. enterica 19SE belonged to ST26 and had a multi-drug-resistant phenotype. It was confirmed that mcr-9 did not mediate colistin resistance in this study, indicating that its transfer may not facilitate the dissemination of colistin resistance.

Keywords: Molecular genetic; Non-functional; Salmonella enterica; mcr-9.

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • China
  • Colistin / pharmacology*
  • Drug Resistance, Multiple, Bacterial
  • Ethanolaminephosphotransferase / genetics*
  • Ethanolaminephosphotransferase / metabolism
  • Food Microbiology
  • Genes, Bacterial
  • Microbial Sensitivity Tests
  • Milk / microbiology*
  • Phylogeny
  • Plasmids
  • Salmonella typhimurium / drug effects*
  • Salmonella typhimurium / genetics*
  • Salmonella typhimurium / isolation & purification
  • Salmonella typhimurium / metabolism
  • Whole Genome Sequencing

Substances

  • Anti-Bacterial Agents
  • Ethanolaminephosphotransferase
  • Colistin